This invention relates to electrical resistance welding and especially to the welding of nuts (commonly called weld nuts) to a base such as a steel sheet. More particularly, the invention relates to a weld nut supporting and locating device operatively associated with one of the two electrodes, for accurately positioning the nut on the base in proper alignment with the base and the respective electrodes prior to the welding operation.
Weld nuts are commonly attached to sheet metal by resistance welding, usually over an opening in the sheet metal to permit a screw or other fastener to extend through the sheet and into the internal threads of the nut. The weld nuts are usually provided with small projections that rest against one side of the sheet. A pair of opposed welding electrodes come together and engage the sheet and nut respectively positioned therebetween, after which welding current is passed between the electrode contact faces through the nut and metal sheet to heat the projections and weld the projections to the sheet. When the sheet metal has an opening to be aligned with the threaded aperture in the weld nut, one of the electrodes may have a pilot pin for the purpose of properly locating the base sheet relative to electrodes and weld nuts.
One means for properly locating the weld nut relative to the electrodes and the metal sheet is disclosed in U.S. Pat. No. 3,573,423 wherein a vacuum technique is used to hold the weld nut on a movable electrode as the electrode is moved into welding position carrying the nut therewith.
Still another means for attaching weld nuts is disclosed in U.S. Pat. No. 2,731,535 wherein a weld nut is located over an opening in the sheet metal by a centering element located in the lower electrode that contacts the sheet. The centering element has a pilot that extends vertically upward through the sheet and into the aperture in the nut and thereby positions the nut prior to the welding operation. Both of the above techniques are effective for attaching weld nuts to sheet metal, however, they each have certain disadvantages such as limitations as to speed of operation, etc.
The method and apparatus of the present invention provide an improved means for carrying and positioning a weld nut prior to its attachment to a base, and afford other features and advantages not obtainable from the prior art.